How to take payment from the client at the end of the work?

[prang153]

I received an order for Google Tag Manager setup Last week. While I was working, I saw my client's website had a problem, due to which I could not complete the order requirements. I told my client about this problem and I said "I can solve this problem, but you have to pay extra for this". 
My client said to me, "I don't have enough hand cash right now. Can you please solve this problem now? I will pay on the 11th of next month."
Then I fixed it and delivered my ongoing order.

Now how to get that fee (extra) from him?

[imagination7413]

Better hope he'll hold to his word. 

Craft a custom order from your inbox, detail the extra work you did, and reference the original order number. If the Buyer accepts, deliver documentation of the work you did (proof of work completed). 

[farhadkhan424]

10 hours ago, prang153 said:

I received an order for Google Tag Manager setup Last week. While I was working, I saw my client's website had a problem, due to which I could not complete the order requirements. I told my client about this problem and I said "I can solve this problem, but you have to pay extra for this". 
My client said to me, "I don't have enough hand cash right now. Can you please solve this problem now? I will pay on the 11th of next month."
Then I fixed it and delivered my ongoing order.

Now how to get that fee (extra) from him?

you should extend the time delivery about next 2 month